1. Field of the Invention
The present invention relates to a structure of an electromagnetic controlled fuel injection apparatus using a unit injection pump composed such that fuel injection timing thereof is controlled by means of an open/close valve which is reciprocated by a solenoid device to open or close the passage between the fuel passage communicating with the plunger room where fuel is received and compressed and the spill passage connecting to the fuel return line.
2. Description of the Related Art
An electromagnetic controlled unit injection pump applied to a diesel engine is composed such that fuel injection timing is controlled through shutting-off/allowing communication of the fuel passage connecting to a plunger room where fuel is introduced and compressed with the spill passage connecting to the fuel return line by closing/opening a poppet valve reciprocated by means of a solenoid device.
Two stage fuel injection consisting of initial injection and primary injection has been proposed for a diesel engine equipped with an electromagnetic controlled fuel injection apparatus like this in order to reduce NOx(nitrogen oxide) and improve combustion efficiency.
An electromagnetic controlled unit injection apparatus has been proposed, which is composed to perform two stage fuel injection like this by providing two solenoid devices for one plunger unit as shown in FIG. 5.
In FIG. 5, reference numeral 40 is a plunger unit, in which fuel fed into a plunger room 6 is compressed to high pressure by a plunger 5 reciprocating in a barrel 7 for the compressed fuel to be supplied to a fuel injection nozzle not shown in the drawing.
Reference numerals 20 are two solenoid devices connected to said plunger unit 40, reference numerals 011 are poppet valve devices accommodated in valve cases 012 and reciprocated by the solenoid devices 20. The plunger room 6 of the plunger unit 40 is communicated to the poppet valve devices 011 through fuel passages bored in the barrel 7 of the plunger unit 40 and by means of fuel pipes 015. Reference numerals 013 are spill passages for spilling fuel to flow out.
In the unit injection pump like this, fuel injection timing is controlled by opening/closing the poppet valves of the poppet valve devices 011, the poppet valves being reciprocated by switching the state of the solenoid devices 20 between excited and non-excited state to be opened/closed for shutting-off/allowing communication of the passages in the fuel pipes 015 and fuel passages 014, which communicate with the plunger room 6 where fuel is introduced and compressed by the reciprocation of the plunger 5 of the plunger unit 40, with the spill passages 013 connecting to the fuel return line.
Two-stage injection consisting of initial injection and primary injection is realized by a single plunger unit through causing time difference between the opening/closing timing of the two poppet valve devices 011 by changing the timing of switching between excited and non-excited state of the two solenoid devices.
In JP7-269438A is disclosed an electromagnetic controlled fuel injection apparatus, in which the opening stroke of the poppet valve is increased at the injection end to allow a rapid pressure drop at the injection end so as to sharpen injection cutoff, while the closing stroke of the poppet valve is shortened.
In the conventional electromagnetic controlled unit injection pump shown in FIG. 5, a single plunger unit 40 is connected to two assembled units each consisting of a solenoid device 20 and a poppet valve device by means of long fuel passages each consisting of a fuel pipe 015 and a fuel passage 014, so a large space is required for installing the electromagnetic controlled unit injection pump, which involves difficulty to mount the injection pump on the upper surface of the crankcase where space is particularly restricted.
Further, in the conventional electromagnetic controlled unit injection pump, as a single plunger unit 40 is connected to two assembled units each consisting of a solenoid device 20 and a poppet valve device by means of long fuel passages each consisting of a fuel pipe 015 and a fuel passage 014, the speed of response of fuel injection in two-stage injection to the switching of the state of the solenoid devices 20 between excited and non-excited state is lowered, it is difficult to obtain a desirable injection mode of two-stage injection with good injection cutoff, and reduction in NOx(nitrogen oxide) and maintenance of engine performance become difficult.
In said JP7-269438A discloses an electromagnetic controlled fuel injection apparatus with which the opening and closing stroke of the poppet valve are controlled, but does not disclose a means to achieve a two-stage injection mode with good injection cutoff by connecting two assembly units consisting of a solenoid device and poppet valve device to a single plunger unit.